Please do not fret. Just because you are not seeing any milk when you pump does not mean you are not producing. I am now nursing my third child. None of my kids have had a drop of formula. I know I product fine. BUT I am not a good pumper. It takes a long time to get any substantial amount. Your baby is MUCH more efficient at getting your milk than a mechanical pump, so fear not.
Also, he chugged that entire bottle b/c bottles are so easy. They don't require the effort that nursing does. So do not take that as a sign that he prefers the formula or that he was famished. It was just easy for him.
Honestly, if you want to have your husband take a turn, pump milk and let him feed the baby that. Formula will ultimately interfere with your nursing schedule and supply. But don't worry. You didn't mess up your supply with one feeding! Just get back to nursing often and you and your son will both benefit. He sounds perfectly healthy and a great little nurser!
OH....finally...more practice pumping will help you get more out. You have to relax and maybe your first time you were a little tense?
You are doing a great job, it sounds like to me. Keep it up!